Anatomy chapter 9

what are the three types of muscles?

skeletal, cardiac, and smooth

where is skeletal located ?

organs attached to bones and skin

where is smooth located?

walls of hollow tubes and organs

where is cardiac located?

heart walls

is skeletal striated? branched? voluntary? need NS stimulation?

striated, not branched, voluntary, yes NS stimulation

is smooth striated? branched? voluntary? need NS stimulation?

not striated, not branched, involuntary, no NS stimulation

is cardiac striated? branched? voluntary? need NS stimulation?

striated, branched, involuntary, no NS stimulation

what are the four important characteristics of muscle tissues?

excitability, contractility, extensibility, elasticity

what are the four important functions of muscle tissues?

moving bones or fluids, maintaining posture, stabilizing joints, heat generation

what is the relationship between muscles, muscle fascicles, and muscle fibers?

A muscle is made up of multiple bundles (muscle fascicles), which are composed of individual muscle fibers.

which connective tissue sheath surrounds each muscle fiber?

endomysium

which connective tissue sheath surrounds each muscle fascicle?

perimysium

which connective tissue sheath surrounds each muscle?

epimysium

what is the special name given to the plasma membrane of a muscle fiber?

sarcolemma

what is the name given to bundles of myofilaments found inside muscle fibers?

myofibril

what is a sarcomere?

contractile unit of striated muscle; composed of myofilaments

which two myofilaments overlap to create a sarcomere?

thick filaments and thin filaments

in which segment of a sarcomere do we find only thick filaments?

H zone

in which segment of a sarcomere do we find only thin filaments?

I band

in which segment of a sarcomere do we find both thick and thin filaments?

A band

what protein makes up thick filaments?

myosin protein

what protein makes up thin filaments?

actin protein

which structure of a thick filament is able to bind to the actin of a thin filament?

myosin heads

what is the sarcoplasmic reticulum (SR)

network of smooth ER

what is the function of the sarcoplasmic reticulum (SR)?

regulates sarcoplasmic calcium levels (stores and releases calcium)

what are T-tubules?

continuations of sarcolemma (cell membrane)

what is the function of T-tubules?

conduct electrical impulses from muscle fiber surface to its core

what is the function of sarcomeres in the sliding filament model of contraction?

the sarcomere shortens

what is the function of myofilaments in the sliding filament model of contraction?

sliding past eachother

what happens to the distance between the sarcomere’s z-discs and M-line during muscle contraction?

decreases

what are the four stages of skeletal muscle contraction?

motor neuron excitation and release of acetylcholine

muscle fiber stimulation by acetylcholine

muscle fiber excitation-contraction coupling

sarcomere contraction occurs by cross-bridge cycling

which two cells are required for skeletal muscle contraction?

motor neuron and acetylcholine

what are the six steps that happen at the neuromuscular junction that lead to excitation of the skeletal muscle fiber?

action potential arrives at axon terminal

voltage gated calcium channels open, ca enters motor neuron

ca entry causes release of ACh neurotransmitter into synaptic cleft

ACh diffuses across to ACh receptors on sarcolemma at neuromuscular junction

ACh binding to receptors, opens gates, allowing soidum to enter resulting in end plate potential

acetylcholinesterase degrades ACh

what is an action potential?

a massive all or none depolarization of a cell’s membrane

do neurons experience AP?

yes

do skeletal muscle cells experience AP?

yes

what are three phases of an action potential?

depolarization, repolarization, hyperpolarization

what is an end plate potential?

(the first step to AP generation in muscle fibers)

ACh binding opens chemically ligand gated ion channels

simultaneous diffusion of Na+ (inward) and K+ (outward)

more Na+diffuses in, so interior of sarcolemma becomes less negative

how is end plate potential related to an action potential in a muscle fiber?

initiates a propagated action potential in the muscle fiber which is accompanied by a mechanical response consisting of an all-or-nothing twitch

what is excitation-contraction coupling?

events that transmit action potential along sarcolemma leading to sliding myofilaments

what are the four steps of E-C coupling?

AP propagated along sarcolemma to T tubules

Voltage sensitive proteins stimulate Ca2+ release from SR

Ca binds to toponin on thin filaments

contraction begins by cross bridge cycling

what are the five steps of ion channel involved in muscle fiber excitation and EC coupling?

Step 1: Action potential arrives at the neuromuscular junction:

Step 2: Action potential propagates along the sarcolemma and into T-tubules:

Step 3: Voltage-gated dihydropyridine receptors (DHPRs) sense depolarization:

Step 4: DHPRs interact with ryanodine receptors (RyR) to release calcium:

Step 5: Calcium binds to troponin, triggering muscle contraction:

what is the purpose of the cross-bridge cycle?

demonstrates the shortening of muscles due to the movement of the contractile proteins

what are the four steps of a cross-bridge cycle?

Cross bridge formation, working (power) stroke, cross bridge detachment, cocking of myosin head

what is triggered when ATP binds to the myosin head?

the detachment of the myosin head from the actin filament

what is triggered when ATP hydrolysis occurs?

the release of the myosin head from the actin filament

which event of the cross-bridge cycle cannot occur in the absence of ATP? what is that condition called?

rigor mortis

what is the name for a skeletal muscle fiber’s tiny response to a single action potential?

muscle twitch

what are the three phases of a muscle twitch?

one action potential occurs

muscle fibers in that one motor unit are excited

that motor unit contracts

what is a motor unit?

one motor neuron and all the skeletal muscle fibers that it innervates

how many motor neurons are involved in one motor unit?

a single motor neuron

how many skeletal muscle fibers are involved in one motor unit?

many

which molecular event is occuring inside a muscle fiber during the latent period of a twitch?

molecular events of EC coupling are occuring

which molecular event is occuring inside a muscle fiber during the contraction period twitch?

cross bridge cycling occurs

what happens to the muscle fiber during the relaxation period of a twitch?

calcium reenters the sarcoplasmic reticulum

how do individual muscle twitches contribute to larger muscle contractions that generate more tension?

If the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger.

what is summation?

the additive effect of several electrical impulses on a neuromuscular junction, the junction between a nerve cell and a muscle cell.

how does the frequency of motor neuron activation relate to summation?

If the frequency of motor neuron signaling increases, summation and subsequent muscle tension in the motor unit continues to rise until it reaches a peak point.

how does simultaneous activation of motor units relate to the tension produced by a skeletal muscle?

increasing activation of motor units produces an increase in muscle contraction known as recruitment.

in what way is an isometric contraction different than an isotonic contraction of skeletal muscle?

isometric- muscle contracts without shortening (tension does not exceed load)

isotonic- muscle contracts with shortening (tension exceeds load)

what are the two types of isotonic contractions?

concentric and eccentric

what are the three main mechanisms for ATP regeneration in skeletal muscles?

direct phosphorylation, anaerobic metabolism, aerobic metabolism

what is an advantage of each mechanism?

direct phosphorylation- makes atp and creatine (provides extra 15 s)

anaerobic metabolism- produced through gylcosis (provides extra 40 s of energy)

aerobic metabolism- produced cellular respiration (provides Extra hours of energy)

what is a disadvantage of each mechanism?

direct phosphorylation- low output

anaerobic metabolism- low output

aerobic metabolism- slow output

which two substrates are needed for ATP regeneration by direct phosphorylation?

ATP and creatine

which sugar is needed for ATP regeneration by anaerobic metabolism?

glycosis

is oxygen required for ATP regeneration by aerobic metabolism? Which organelle is also needed?

yes needs o2 and mitochondria

which mechanism for ATP regeneration will be dominant during each phase of exercise? next 10 seconds? next few minutes? next minutes to hours?

seconds- direct phosphorylation

minutes- anaerboic

hours- aerobic

what does EPOC stand for?

excess post exercise oxygen consumption

what are four events happening in a persons body while they experience EPOC?

muscle o2 stores restored

lactic acid converted to pyruvic acid

glucose stored as glycogen

atp and creatine phosphate stores restored

what is muscle fatigue?

how does it protect a persons body?

physiological inability to contract even when muscle is stimulated

-prevents complete depletion of ATP

- happens quickly w intense exercise

-happens slowly w low intensity exercise

what are two major causes of muscle fatigue?

ion imbalances

decreased glycogen stores

what are four factors that can increase the force of a skeletal muscle contraction?

high frequency stimulation

large # of muscle fibers recruited

large muscle fibers

muscle and sarcomere stretched to slightly over 100% of resting length

what are three factors that can increase the velocity and duration of a skeletal muscle contraction?

load

motor unit recruitment

muscle fiber types recruited

what are three types of skeletal muscle fiber?

slow oxidative fibers

fast oxidative fibers

fast gylcolytic fibers

what two characteristics are used to organize the three types of skeletal muscle fiber?

contraction speed and main ATP source

which type contracts most quickly?

most slowly?

slow: slow oxidative fibers

fast: fast oxidative fibers

fastest: fast glycolytic fibers

which type fatigues most quickly?

most slowly?

slow: slow oxidative

intermediate: fast oxidative

fast: fast gylcolytic

which type produces the most force?

the least?

low: slow oxidative

medium: fast oxidative

high: fast glycoytic

what are three adaptations that will occur in response to endurance exercise?

muscle capillaries increase

#of mitochondria

myoglobin synthesis increases

what are five adaptations that will occur in response to resistance exercise?

muscle fiber size increases

#of mitochondria increase

gylcogen stores increase

#of myofilaments increase

connective tissues increase